1. Field of the Invention
The present invention generally relates to the field of light-emitting devices. More particularly, the present invention relates to a light-emitting device with a 3-dimensional distributed Bragg reflector (DBR).
2. Description of the Prior Art
A light-emitting diode (LED) is a solid-state semiconductor light source that is fabricated with semiconductor materials. LEDs are used in applications as diverse as: replacements for aviation lighting, automotive lighting (particularly for indicators) and in traffic signals. The compact size of LEDs has allowed new text and video display or sensor devices to be developed, with their quick switching rates being very useful for advanced communication technology.
A structure of a conventional light-emitting device generally includes a substrate, an epitaxial structure disposed on the substrate, a P-side electrode pad electrically connected to a P-type semiconductor contact layer located in the epitaxial structure, a N-side electrode pad electrically connecting to a N-type semiconductor contact layer located in the epitaxial structure, an active layer disposed between the P-type semiconductor contact layer and the N-type semiconductor contact layer. In addition, a transparent conductive layer (TCL) is usually disposed between the P-side electrode pad and the P-type semiconductor contact layer in order to create an ohmic contact.
According to a prior art disclosed in U.S. Pub. No. 2008/0064133 A1, a flip-chip type nitride light-emitting device has a mesh-type DBR disposed between a P-side electrode and a P-type nitride semiconductor layer. The mesh-type DBR has a plurality of mesh-like openings, exposing parts of the P-type nitride semiconductor layer and extended on the top surface of the P-type nitride semiconductor layer in a two-dimensional direction. An ohmic contact layer is provided to cover the mesh-type DBR and fill up the mesh-like openings so that the surface of the P-type nitride semiconductor layer not covered by the mesh-type DBR may be in contact directly with the ohmic contact layer. The P-side electrode is disposed on the ohmic contact layer. The composition of the above-mentioned ohmic contact layer comprises nickel, silver, aluminum or other similar metals, and the configuration of the mesh-type DBR is an AlGaN/GaN stack structure. Both of the ohmic contact layer and mesh-type DBR have a high reflectivity, so that light emitted from the active layer may be reflected by these highly reflective components and emit from a top surface of a transparent substrate.
T.W. Pub. No. 200921 931 discloses another flip-chip type light-emitting device. The characteristic of the light-emitting device is that a P-side electrode and an N-side electrode are disposed on the same level, so that the distance between the P-side electrode and the N-side electrode can be shortened. The light-emitting device has a reflector layer formed under the P-side electrode via thermal evaporation, electron-beam deposition, or sputter deposition. Since the P-side electrode has to be electrically connected to a contact layer, the reflector must be composed of conductive materials.